Method and device for forming metal gate electrodes for transistors

ABSTRACT

A semiconductor device includes a first transistor and a second transistor. The first transistor includes: a first source and a first drain separated by a first distance, a first semiconductor structure disposed between the first source and first drain, a first gate electrode disposed over the first semiconductor structure, and a first dielectric structure disposed over the first gate electrode. The first dielectric structure has a lower portion and an upper portion disposed over the lower portion and wider than the lower portion. The second transistor includes: a second source and a second drain separated by a second distance greater than the first distance, a second semiconductor structure disposed between the second source and second drain, a second gate electrode disposed over the second semiconductor structure, and a second dielectric structure disposed over the second gate electrode. The second dielectric structure and the first dielectric structure have different material compositions.

PRIORITY DATA

The present application is a divisional of U.S. patent application Ser.No. 16/370,258, filed on Mar. 29, 2019, which claims priority to U.S.Provisional Patent Application No. 62/736,087, filed on Sep. 25, 2018,entitled “METHOD AND DEVICE FOR FORMING METAL GATE ELECTRODES FORTRANSISTORS”, the disclosures of which are hereby incorporated byreference in their entirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs where each generation has smaller and more complexcircuits than the previous generation. However, these advances haveincreased the complexity of processing and manufacturing ICs and, forthese advances to be realized, similar developments in IC processing andmanufacturing are needed. In the course of IC evolution, functionaldensity (i.e., the number of interconnected devices per chip area) hasgenerally increased while geometry size (i.e., the smallest componentthat can be created using a fabrication process) has decreased.

The decreased geometry sizes lead to challenges in semiconductorfabrication. For example, as geometry sizes continue to decrease,loading (e.g., due to components having different sizes) may become aconcern. For example, loading issues could lead to excessive loss of agate height of a transistor. When this occurs, the result is degradeddevice performance or even device failures.

Therefore, while existing semiconductor devices and the fabricationthereof have been generally adequate for their intended purposes, theyhave not been entirely satisfactory in every aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a perspective view of an example FinFET device.

FIGS. 2A-33A, 2B-33B, 2C-33C, and 2D-33D are cross-sectional views ofsemiconductor devices at various stages of fabrication according tovarious embodiments of the present disclosure.

FIG. 34 is a flow chart of a method for fabricating a semiconductordevice in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

It is understood that the following disclosure provides many differentembodiments, or examples, for implementing different features of thepresent disclosure. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Forexample, the formation of a first feature over or on a second feature inthe description that follows may include embodiments in which the firstand second features are formed in direct contact, and may also includeembodiments in which additional features may be formed between the firstand second features, such that the first and second features may not bein direct contact. In addition, the present disclosure may repeatreference numerals and/or letters in the various examples. Thisrepetition is for the sake of simplicity and clarity and does not initself dictate a relationship between the various embodiments and/orconfigurations discussed. Moreover, various features may be arbitrarilydrawn in different scales for the sake of simplicity and clarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,elements described as being “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term “below” can encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly.

Still further, when a number or a range of numbers is described with“about,” “approximate,” and the like, the term is intended to encompassnumbers that are within a reasonable range including the numberdescribed, such as within +/−10% of the number described or other valuesas understood by person skilled in the art. For example, the term “about5 nm” encompasses the dimension range from 4.5 nm to 5.5 nm.

The present disclosure is directed to, but not otherwise limited to, amethod to perform semiconductor fabrication, for example an aspect ofsemiconductor fabrication pertaining to metal gate electrode formation.To illustrate the various aspects of the present disclosure, a FinFETfabrication process is discussed below as a non-limiting example. Inthat regard, a FinFET device is a fin-like field-effect transistordevice, which has been gaining popularity in the semiconductor industry.The FinFET device may be a complementary metal-oxide-semiconductor(CMOS) device including a P-type metal-oxide-semiconductor (PMOS) FinFETdevice and an N-type metal-oxide-semiconductor (NMOS) FinFET device. Thefollowing disclosure will continue with one or more FinFET examples toillustrate various embodiments of the present disclosure, but it isunderstood that the application is not limited to the FinFET device,except as specifically claimed. In other words, the various aspects ofthe present disclosure may be applied in the fabrication oftwo-dimensional planar transistors too.

Referring to FIG. 1 , a perspective view of an example FinFET device 10is illustrated. The FinFET device structure 10 includes a N-type FinFETdevice structure (NMOS) 15 and a P-type FinFET device structure (PMOS)25. The FinFET device structure 10 includes a substrate 52. Thesubstrate 52 may be made of silicon or other semiconductor materials.Alternatively or additionally, the substrate 52 may include otherelementary semiconductor materials such as germanium. In someembodiments, the substrate 52 is made of a compound semiconductor suchas silicon carbide, gallium arsenic, indium arsenide, or indiumphosphide. In some embodiments, the substrate 52 is made of an alloysemiconductor such as silicon germanium, silicon germanium carbide,gallium arsenic phosphide, or gallium indium phosphide. In someembodiments, the substrate 52 includes an epitaxial layer. For example,the substrate 52 may include an epitaxial layer overlying a bulksemiconductor.

The FinFET device structure 10 also includes one or more fin structures54 (e.g., Si fins) that extend from the substrate 52 in the Z-directionand surrounded by spacers 55 in the Y-direction. The fin structures 54are elongated in the X-direction and may optionally include germanium(Ge). The fin structure 54 may be formed by using suitable processessuch as photolithography and etching processes. In some embodiments, thefin structure 54 is etched from the substrate 52 using dry etch orplasma processes. In some other embodiments, the fin structure 54 can beformed by a double-patterning lithography (DPL) process. DPL is a methodof constructing a pattern on a substrate by dividing the pattern intotwo interleaved patterns. DPL allows enhanced feature (e.g., fin)density. The fin structure 54 also includes an epi-grown material 12,which may (along with portions of the fin structure 54) serve as thesource/drain of the FinFET device structure 10.

An isolation structure 58, such as a shallow trench isolation (STI)structure, is formed to surround the fin structure 54. In someembodiments, a lower portion of the fin structure 54 is surrounded bythe isolation structure 58, and an upper portion of the fin structure 54protrudes from the isolation structure 58, as shown in FIG. 1 . In otherwords, a portion of the fin structure 54 is embedded in the isolationstructure 58. The isolation structure 58 prevents electricalinterference or crosstalk.

The FinFET device structure 10 further includes a gate stack structureincluding a gate electrode 60 and a gate dielectric layer (not shown)below the gate electrode 60. The gate electrode 60 may includepolysilicon or metal. Metal includes tantalum nitride (TaN), nickelsilicon (NiSi), cobalt silicon (CoSi), molybdenum (Mo), copper (Cu),tungsten (W), aluminum (Al), cobalt (Co), zirconium (Zr), platinum (Pt),or other applicable materials. Gate electrode 60 may be formed in a gatelast process (or gate replacement process). Hard mask layers 62 and 64may be used to define the gate electrode 60. A dielectric layer 65 mayalso be formed on the sidewalls of the gate electrode 60 and over thehard mask layers 62 and 64.

The gate dielectric layer (not shown) may include dielectric materials,such as silicon oxide, silicon nitride, silicon oxynitride, dielectricmaterial(s) with high dielectric constant (high-k), or combinationsthereof. Examples of high-k dielectric materials include hafnium oxide,zirconium oxide, aluminum oxide, hafnium dioxide-alumina alloy, hafniumsilicon oxide, hafnium silicon oxynitride, hafnium tantalum oxide,hafnium titanium oxide, hafnium zirconium oxide, the like, orcombinations thereof.

In some embodiments, the gate stack structure includes additionallayers, such as interfacial layers, capping layers, diffusion/barrierlayers, or other applicable layers. In some embodiments, the gate stackstructure is formed over a central portion of the fin structure 54. Insome other embodiments, multiple gate stack structures are formed overthe fin structure 54. In some other embodiments, the gate stackstructure includes a dummy gate stack and is replaced later by a metalgate (MG) after high thermal budget processes are performed.

The gate stack structure is formed by a deposition process, aphotolithography process and an etching process. The deposition processincludes chemical vapor deposition (CVD), physical vapor deposition(PVD), atomic layer deposition (ALD), high density plasma CVD (HDPCVD),metal organic CVD (MOCVD), remote plasma CVD (RPCVD), plasma enhancedCVD (PECVD), plating, other suitable methods, and/or combinationsthereof. The photolithography processes include photoresist coating(e.g., spin-on coating), soft baking, mask aligning, exposure,post-exposure baking, developing the photoresist, rinsing, drying (e.g.,hard baking). The etching process includes a dry etching process or awet etching process. Alternatively, the photolithography process isimplemented or replaced by other proper methods such as masklessphotolithography, electron-beam writing, and ion-beam writing.

FinFET devices offer several advantages over traditional Metal-OxideSemiconductor Field Effect Transistor (MOSFET) devices (also referred toas planar transistor devices). These advantages may include better chiparea efficiency, improved carrier mobility, and fabrication processingthat is compatible with the fabrication processing of planar devices.Thus, it may be desirable to design an integrated circuit (IC) chipusing FinFET devices for a portion of, or the entire IC chip.

However, FinFET fabrication may still have challenges. For example,loading may become an issue in processes such as etching, where deviceshaving substantially different sizes may have different etchingperformances. In the formation of metal gate electrodes, conventionalprocesses may form a bulk tungsten material with a wide lateraldimension (e.g., long channel devices) as a part of the metal gateelectrode. This could cause loading issues and may lead to excessiveloss of gate height, particularly if other smaller devices (e.g., shortchannel devices) are present. In addition, conventional processes had toetch a work function metal and the bulk tungsten separately, which addsto the fabrication process complexity and cost.

To reduce the excessive loss of the gate height and to improve loading,the present disclosure utilizes unique fabrication process flows, whichallows the metal gate electrode materials to be etched to not havesubstantially different dimensions from one another. Furthermore, thepresent disclosure allows the work function metal and the metal material(e.g., tungsten) formed above the work function metal to be etchedtogether, which reduces process complexity and cost. The presentdisclosure also forms T-shape helmets having a high-k dielectricmaterial above gate spacers. During the formation of source/draincontacts, a contact hole etching process is supposed to etch aninterlayer dielectric (ILD) material adjacent to the gate spacers toform the contact holes. However, due to the similarity in materialcompositions between the ILD and the gate spacers, the gate spacerscould be inadvertently etched, particularly for short channel deviceswhere an overlay shift may exacerbate this problem. Here, the high-kdielectric material composition of the T-shaped helmet is more resistantto etching and therefore protects the gate spacers underneath from beinginadvertently etched during the contact hole formation.

The various aspects of the present disclosure will now be discussedbelow in more detail with reference to FIGS. 2A-33A, 2B-33B, 2C-33C,2D-33D and 34 below. In that regard, FIGS. 2A-33A illustrate fragmentarycross-sectional side views of a portion of a FinFET device 100A atvarious stages of fabrication, FIGS. 2B-33B illustrate fragmentarycross-sectional side views of a portion of a FinFET device 100B atvarious stages of fabrication, FIGS. 2C-33C illustrate fragmentarycross-sectional side views of a portion of a FinFET device 100C atvarious stages of fabrication, and FIGS. 2D-33D illustrate fragmentarycross-sectional side views of a portion of a FinFET device 100D atvarious stages of fabrication. It is understood that the cross-sectionalviews of FIGS. 2A-33A, 2B-33B, 2C-33C, and 2D-33D correspond to thecross-sectional views taken in the X-direction shown in FIG. 1 , and assuch they may be referred to as X-cuts.

The FinFET devices 100A, 100B, 100C, and 100D may be devices on the samewafer but may have different sizes, for example different gate lengths(Lag). In the illustrated embodiment, the FinFET device 100A has thesmallest gate length (e.g., physical Lg in a range between about 8 nmand about 20 nm), the FinFET device 100B has a gate length (e.g., Lg ina range between about 20 nm and about 44 nm) larger than the gate lengthof the FinFET device 100A, the FinFET device 100C has a gate length(e.g., physical Lg in a range between about 44 nm and about 72 nm)larger than the gate length of the FinFET device 100B, and the FinFETdevice 100D has the largest gate length (e.g., physical Lg in a rangebetween about 72 nm and about 240 nm). The FinFET device 100A may bereferred to as a short channel (SC) device. The FinFET devices 100B and100C may each be referred to as middle channel (SC) device. The FinFETdevice 100D may be referred to as a long channel (LC) device.

Due to their differences in size, the FinFET device 100A, 100B, 100C,and 100D may have different applications or may be used differently onan IC. As a non-limiting example, the short channel FinFET device 100Amay be suitable for “core” devices, which may include logic devices(that do not need to handle the input/output voltages/currentsdirectly), such as the various logic gates such as NAND, NOR, INVERTER,etc. In some embodiments, the core devices may include transistors of astatic random-access memory (SRAM) device. In comparison, the longchannel FinFET device 100D may include, as non-limiting examples,input/output (I/O) devices that are configured to handle the inputand/or output voltages/currents, and as such they need to be able totolerate a greater amount of voltage or current swing than non-I/Odevices. The middle channel FinFET devices 100B and 100C may be used forother suitable IC applications.

Referring now to FIGS. 2A, 2B, 2C, and 2D, the FinFET devices 100A,100B, 100C, and 100D include fin structures 110A, 110B, 110C, and 110D,respectively. The fin structures 110A, 110B, 110C, and 110D may each besimilar to the fin structure 104 discussed above with reference to FIG.1 . The fin structures 110A, 110B, 110C, and 110D may include asemiconductor material such as silicon or silicon germanium. In someembodiments, the fin structures 110A-110D may serve as channel regionsof transistors.

The FinFET devices 100A, 100B, 100C, and 100D also include source/drainregions 120A, 120B, 120C, and 120D, respectively. The source/drainregions 120A, 120B, 120C, and 120D may each include a dopant, forexample boron, arsenic, phosphorous, etc., depending on whether therespective FinFET device is a P-type transistor or an N-type transistor.In some embodiments, the gate length Lg of the respective FinFET device100A, 100B, 100C, and 100D roughly correspond to distances 125A, 125B,125C, and 125D between the two adjacent source/drain regions for theFinFET devices 100A, 100B, 100C, and 100D, respectively. As such, theFinFET device 100A has the most closely located source/drain regions120A (e.g., 125A being the smallest), the FinFET device 100B hassource/drain regions 120B that are farther apart (e.g., 125B>125A), theFinFET device 100C has source/drain regions 120C that are even fartherapart (e.g., 125C>125B>125A), and the FinFET device 100D has the mostspaced-apart source/drain regions 120D (e.g., 125D>125C>125B>125A).

The FinFET devices 100A, 100B, 100C, and 100D include interlayerdielectric (ILD) layers 130A, 130B, 130C, and 130D, respectively. TheILD layers 130A, 130B, 130C, and 130D may each be a bottommost ILD layerand may be referred to as ILD0 layers. The ILD layers 130A, 130B, 130C,and 130D each include a dielectric material, for example a low-kdielectric material (e.g., a dielectric material having a smallerdielectric constant than silicon oxide) in some embodiments, or siliconoxide in some other embodiments. The ILD layers 130A, 130B, 130C, and130D are disposed over, and vertically aligned with, the source/drainregions 120A, 120B, 120C, and 120D, respectively.

The FinFET devices 100A, 100B, 100C, and 100D include work functionmetal layers 140A, 140B, 140C, and 140D, respectively. The workfunctional metal layers 140A, 140B, 140C, and 140D are configured totune a work function of their corresponding FinFET device to achieve adesired threshold voltage Vt. In various embodiments, the work functionmetal layers 140A, 140B, 140C, and 140D may contain: TiN, TaN, TiAl,TiAlN, or TaCN, or combinations thereof. The work function metal layers140A, 140B, 140C, and 140D are disposed over, and vertically alignedwith, the fin structures 110A, 110B, 110C, and 110D, respectively.

The FinFET devices 100A, 100B, 100C, and 100D include spacers 150A,150B, 150C, and 150D, respectively. The spacers 150A are disposedbetween the ILD layer 130A and the work function metal layers 140A. Thespacers 150B are disposed between the ILD layer 130B and the workfunction metal layer 140B. The spacers 150C are disposed between the ILDlayer 130C and the work function metal layers 140C. The spacers 150D aredisposed between the ILD layer 130D and the work function metal layers140D. The spacers 150A, 150B, 150C, and 150D include a dielectricmaterial, for example, a low-k dielectric material in some embodiments,or silicon nitride (SiNx), silicon carbon nitride (SiCN), siliconoxynitride (SiON), silicon oxycarbide nitride (SIOCN), or combinationsthereof in other embodiments. The spacers 150A, 150B, 150C, and 150C mayeach be formed by a deposition process followed by one or more etchingand polishing processes. If not sufficiently protected, the spacer 150Amay become inadvertently damaged during source/drain contact holeetching processes performed later. According to the various aspects ofthe present disclosure, a T-shaped helmet may be formed to protect thespacers 150A from etching damages, as discussed below in more detail.

The FinFET devices 100A, 100B, 100C, and 100D include metal layers 160A,160B, 160C, and 160D, respectively. The metal layers 160A, 160B, 160C,and 160D are formed over the work function metal layers 140A, 140B,140C, and 140D, respectively. The work function metal layers 140A, 140B,140C, 140D and the metal layers 160A, 160B, 160C, and 160D collectivelyform the gate electrodes of the FinFET devices 100A, 100B, 100C, and100D, respectively. In some embodiments, the metal layers 160A, 160B,160C, and 160D include tungsten (W). In some embodiments, the metallayers 160A, 160B, 160C, and 160D are formed by atomic layer deposition(ALD). In some embodiments, the metal layers 160A, 160B, 160C, and 160Dmay have a thickness that is in a range between about 30 angstroms andabout 150 angstroms. Compared to conventional processes where a bulktungsten is formed (with a much greater thickness), the thickness of themetal layers 160A-160D is substantially smaller, which makes it easierto etch in later processes, as well as reducing etching loadingconcerns.

The FinFET devices 100A, 100B, 100C, and 100D have gate heights 170A,170B, 170C, and 170D, respectively. The gate heights 170A, 170B, 170C,and 170D may approximately correspond to the vertical dimensions of thespacers 150A, 150B, 150C, and 150D, respectively. In some embodiments,the gate heights 170A, 170B, 170C, and 170D may be in a range betweenabout 60 nm and about 120 nm.

As shown in FIGS. 2A-2D, the size differences (e.g., different gatelengths Lg) between the FinFET devices 100A, 100B, 100C, and 100D leadto the different shapes or cross-sectional profiles between the workfunction metal layers 140A, 140B, 140C, 140D, as well as differentshapes or cross-sectional profiles between the metal layers 160A, 160B,160C, 160D. For example, since the FinFET device 100A has the shortestgate length, the portions of the work function metal layer 140A disposedon sidewalls of the spacers 150A merge together, while an upper portionof the work function metal layer 140A is disposed above the ILD layer130A and the spacers 150A.

In comparison, the FinFET device 100B has a longer gate length than theFinFET device 100A, and thus the portions of the work function metallayer 140B disposed on sidewalls of the spacers 150B do not mergetogether, but rather define an opening. This opening is then filled by aportion of the metal layer 160B.

For the FinFET device 100C, it has an even longer gate length than theFinFET device 100B. Similar to the FinFET device 100B, the portions ofthe work function metal layer 140C disposed on sidewalls of the spacers150C do not merge together but define an opening, which is partiallyfilled by the metal layer 160C. However, due to the longer gate lengthof the FinFET device 100C, the opening defined by the work functionmetal layer 140C is sufficiently wide, such that the metal layer 160Cdoes not completely fill it. Instead, the portions of the metal layer160C disposed on the sidewalls of the work function metal layer 140Cdefine an opening 180C.

Meanwhile, the FinFET device 100D has the longest gate length, andsimilar to the FinFET device 100C, the FinFET device 100D also has anopening 180D defined by the portions of the metal layer 160D that aredisposed on the sidewalls of the work function metal layer 140D.Alternatively stated, the metal layers 140D and 160 partially, but donot completely, fill the opening defined by the sidewalls of the spacers150D and the upper surface of the fin structure 110D, and by doing so,the metal layer 160D defines the opening 180D.

Referring now to FIGS. 3A-3D, dielectric layers 210A, 210B, 210C, and210D are formed over the metal layers 160A, 160B, 160C, and 160D,respectively. The dielectric layers 210A-210D may be formed by asuitable deposition process, for example by ALD. In some embodiments,the dielectric layers 210A-210D include silicon nitride. In otherembodiments, the dielectric layers 210A-210D may include silicon oxide.Note that for FinFET devices 100C and 100D, the dielectric layer 210Cand 210D fill the openings 180C and 180D, respectively. Thereafter,dielectric layers dielectric layers 220A, 220B, 220C, and 220D areformed over the dielectric layers 210A, 210B, 210C, and 210D,respectively. The dielectric layers 220A-220D may also be formed by oneor more suitable deposition processes. For example, the dielectriclayers 220A-220D may be formed by ALD, or plasma enhanced chemical vapordeposition (PECVD), or a combination of ALD and PECVD (e.g., a lowerportion being formed by ALD, and an upper portion being formed byPECVD).

The dielectric layers 220A-220D may contain different materials than thedielectric layers 210A-210D. For example, in embodiments where thedielectric layers 210A-210D contain silicon nitride, the dielectriclayers 220A-220D may contain silicon oxide, or vice versa. In otheralternative embodiments, the dielectric layers 210A-210D and thedielectric layers 220A-220D may include the same type of materials. Notethat in the case of FinFET device 100D, the dielectric layer 210D andthe dielectric layer 220D collectively fill the opening 180D.

Referring now to FIGS. 4A-4D, a planarization process such as a chemicalmechanical polishing (CMP) process is performed to the FinFET devices100A-100D. The planarization process removes portions of the dielectriclayers 210A-210D and 220A-220D, as well as portions of the metal layers160A-160D, until the work function metal layers 140A-140D are reached.In other words, the work function metal layers 140A-140D serve aspolishing-stop layers for the planarization process.

Referring now to FIGS. 5A-5D, a dielectric layer 230A is formed over thework function metal layer 140A for the FinFET device 100A. Thereafter,one or more etching processes 235 may be performed to the FinFET devices100B-100D. The dielectric layer 230A serves as an etching mask duringthe one or more etching processes 235 and protects the FinFET device100A from being etched. Meanwhile, the one or more etching processes 235etch away portions of the metal layers 160B-160D and portions of thework function metal layers 140B-140D. In some embodiments, the one ormore etching processes 235 may use one or more of the followingmaterials as etchants: BCl₃, Cl₂, CF₄, NF₃, HBr/NF₃, Cl₂/O₂/N₂/NF₃,CHF₃/H₂/Ar, or combinations thereof.

As a result of the one or more etching processes 235, openings 240B,240C, and 240D are formed in the FinFET devices 100B, 100C, and 100D,respectively. For the FinFET device 100B, the opening 240B exposes aremaining portion of the work function metal layer 140B and a remainingportion of the metal layer 160B. For the FinFET device 100C, the opening240C exposes a remaining portion of the work function metal layer 140Cand a remaining portion of the metal layer 160C. For the FinFET device100D, the opening 240D exposes a remaining portion of the work functionmetal layer 140D and a remaining portion of the metal layer 160D. Thedielectric layer 210C remains in the FinFET device 100C, and thedielectric layers 210D and 220D remain in the FinFET device 100D. It maybe said that the openings 240B, 240C and 240D each have a U-shapedcross-sectional profile, as defined by the upper surfaces of the workfunction metal layers 140B & 160B, 140C &160C, 140D & 160D and the sidesurfaces of the dielectric layers 210C/210D and the spacers 150B, 150C,150D, respectively. The U-shaped cross-sectional profile is anotherunique characteristic of the present disclosure.

The openings 240B, 240C, and 240D have lateral dimensions 245B, 245C,and 245D, respectively, which are not too different from one another.For example, the lateral dimension 245B is in a range between about 20nm and about 42 nm, the lateral dimension 245C is in a range betweenabout 10 nm and about 25 nm, and the lateral dimension 245D is in arange between about 10 nm and about 25 nm. In some embodiments, a ratiobetween the largest one of the lateral dimensions 245B/245C/245D and thesmallest one of the lateral dimensions 245B/245C/245D is in a range fromabout 2:1 and about 1:1.

Due to the similarity between the lateral dimensions 245B-245D, thelateral dimensions for the metal layers 160B-160D and 140B-140D that areetched by the etching processes 235 are not too different from oneanother either. This reduces etching loading problems. For example, ifbulk metal layers had been formed for the FinFET devices 100B, 100C and100D, then the bulk metal layers would have substantially differentlateral dimensions (e.g., FinFET device 100D having the largest bulkmetal layer, and the FinFET device 100B having the smallest metallayer). As a result, the etching of the differently-sized metal layerswould have had substantially different loading, which could lead to lackof uniformity.

Here, the formation of the thin metal layers 160B-160D allows dielectriclayers 210C-210D and 220D to be formed, and the lateral dimensions ofthe metal layers 160B-160D that need to be etched are defined by thesizes 245B-245D of the openings 240B-240D, respectively. Since there isnot a big difference between the lateral dimensions 245B-245D, theetching loading concerns are greatly reduced when the metal layers160B-160D are etched. In addition, the present disclosure allows thework function metal layers 140B-140D and the metal layers 160B-160D tobe etched simultaneously during the etching processes 235, rather thanseparately. This reduces fabrication process complexity and cost.

Referring now to FIGS. 6A-6D, dielectric layers 250A, 250B, 250C, and250D are formed for the FinFET devices 100A, 100B, 100C, and 100D,respectively. The dielectric layer 250A is formed over the dielectriclayer 250A. The dielectric layer 250B is formed over the ILD 130B, thespacers 150B, the work function metal layer 140B, and the metal layer160B, and fills the opening 240B. The dielectric layer 250C is formedover the ILD 130C, the spacers 150C, the work function metal layer 140C,the metal layer 160C, and the dielectric layer 210C, and fills theopening 240C. The dielectric layer 250D is formed over the ILD 130D, thespacers 150D, the work function metal layer 140D, the metal layer 160D,and the dielectric layers 210D-220D, and fills the opening 240D. Thedielectric layers 250A-250D are formed by a suitable deposition processsuch as an ALD process. In some embodiments, the dielectric layers250A-250D include silicon nitride.

Referring now to FIGS. 7A-7D, a planarization process such as a chemicalmechanical polishing (CMP) process is performed to the FinFET devices100A-100D. The planarization process removes portions of the dielectriclayers 250A-250D and the upper portions of the spacers 150A-150D, aswell as the dielectric layer 230A and portions of the work functionmetal layer 140A of FinFET device 100A, until the ILD layers 130A-130Dare reached. In other words, the ILD layers 130A-130D serve aspolishing-stop layers for the planarization process. As a result of theplanarization process, the FinFET devices 100A, 100B, 100C, and 100D nowhave reduced gate heights 270A, 270B, 270C, and 270D, respectively. Thegate heights 270A, 270B, 270C, and 270D may approximately correspond tothe vertical dimensions of the ILD layers 130A, 130B, 130C, and 130D,respectively. In some embodiments, the gate heights 270A, 270B, 270C,and 270D may be in a range between about 45 nm and about 89 nm.

Referring now to FIGS. 8A-8D, one or more etching processes 300 may beperformed to the FinFET devices 100A-100D. The one or more etchingprocesses 300 remove portions of the ILD 130A, 130B, 130C, and 130D toform recesses 310A, 310B, 310C, and 310D in the FinFET devices 100A,100B, 100C, and 100D. The recesses 310A, 310B, 310C, and 310D are etchedto have vertical dimensions 320A, 320B, 320C, and 320D, respectively,which each correspond to a distance from the top surface of therespective ILD layer 130A/B/C/D to a top surface of the respective workfunction metal layer 140A/B/C/D. In some embodiments, the verticaldimensions 320A, 320B, 320C, and 320D are in a range between about 15 nmand about 30 nm.

Referring now to FIGS. 9A-9D, dielectric layers 330A, 330B, 330C, and330D are formed to fill the recesses 310A, 310B, 310C, and 310D,respectively. The dielectric layers 330A, 330B, 330C, and 330D areformed over the ILD layers 130A, 130B, 130C, and 130D, respectively. Thedielectric layers 330A-330D may be formed using a suitable depositionprocess, such as ALD, CVD, etc. In some embodiments, the dielectriclayers 330A-330D may include yttrium silicon oxide (YSiO_(x)). In otherembodiments, the dielectric layers 330A-330D may include silicon nitride(SiN), silicon oxy-carbide (SiOC), silicon carbon nitride (SiCN), orsilicon oxy-carbon nitride (SiOCN). Following the deposition of thedielectric layers 330A-330D, a planarization process such as a CMPprocess may be performed to polish the surface of the dielectric layers330A-330D, until the upper surface of the dielectric layer 330A iscoplanar with the upper surface of the work function metal layers 140A,and the upper surfaces of the dielectric layers 330B-330D are coplanarwith the upper surfaces of the dielectric layers 250B-250D,respectively. The dielectric layers 330A-330D have vertical dimensions340A-340D, respectively. Due to the planarization process removing someportions of the work function metal layer 140A and the dielectric layers250B-250D, the vertical dimensions 340A-340D are smaller than thevertical dimensions 320A-320D. In some embodiments, the verticaldimensions 340A-340D are in a range between about 15 nm and about 21 nm.It is understood that the processes discussed with reference to FIGS.8A-8D and 9A-9D may be optional processes. In other words, they may beperformed in some embodiments but may be omitted in other embodiments,in which case the processes associated with FIGS. 10A-10D (discussedbelow) may be performed after the processes of FIGS. 7A-7D areperformed.

Referring now to FIGS. 10A-10D, one or more etching processes 350 areperformed to the FinFET devices 100A-100D. The one or more etchingprocesses 350 form T-shaped recesses 360A in the FinFET device 100A byremoving portions of the work function metal layer 140A and the spacers150A. For example, in some embodiments, the one or more etchingprocesses 350 may first perform a first etch-back process on the gatemetal in which the work function metal layer 140A is etched away withoutsubstantially etching the spacers 150A. A spacer pull-back process isthen performed to remove portions of the spacers 150A above the workfunction metal layer 140A. Thus, the first etching-back process and thespacer pull-back process effectively define a height of the spacers150A. Thereafter, a second etch-back process is performed to selectivelyremove the work functional metal layer 140A again without substantiallyetching the spacers 150A. The second etch-back process effectivelydefines the height of the (now-shorter) work function metal layer 140A.In other embodiments, the one or more etching processes 350 may includean etching process in which an etching selectivity exists between thespacers 150A and the work function metal layer 140A, such that the workfunction metal layer 140A is etched away at a faster rate while thespacers 150A are etched away at a slower rate. Regardless, the endresult is that, after the one or more etching process 350 are performed,the spacers 150A are taller than the work function metal layers 140A. Asa result, the recesses 360A now have a T-shaped profile in thecross-sectional view of FIG. 10A. The one or more etching processes alsoetch away portions of the dielectric layers 330A-330D. As a result, theFinFET devices 100A-100D now have reduced heights 370A-370D,respectively. In some embodiments, the heights 370A-370D are in a rangebetween about 37 nm to about 74 nm.

Referring now to FIGS. 11A-11D, metal layers 380A are formed over thework function metal layers 140A for the FinFET device 100A. In someembodiments, the metal layers 380A may include the same material as themetal layers 160B-160D, for example they may all include tungsten. Themetal layers 380A and the work function metal layers 140A collectivelyform the gate electrodes of the FinFET device 100A. The metal layers160B-160D and the work function metal layers 140B-140D collectively formthe gate electrodes of the FinFET devices 100B, 100C, and 100D,respectively.

Referring now to FIGS. 12A-12D, dielectric layers 400A, 400B, 400C, and400D are formed for the FinFET devices 100A, 100B, 100C, and 100D,respectively. The dielectric layers 400A are formed over the dielectriclayers 330A, the spacers 150A, and the metal layers 380A and fill theT-shaped recesses 360A. The dielectric layers 400B-400D are formed overthe dielectric layers 330B-330D, the spacers 150B-150D, and thedielectric layers 250B-250D. The dielectric layers 400A-400D may includea high-k dielectric material (e.g., a dielectric material having adielectric constant greater than the dielectric constant of silicondioxide). In some embodiments, the dielectric layers 400A-400D mayinclude zirconium oxide (Sox). In other embodiments, the dielectriclayers 400A-400D may include yttrium silicon oxide (YSiO_(x)), siliconoxy-carbide (SiOC), or another suitable high-k dielectric material.

It is understood that other processes may be performed after the stageof fabrication shown in FIGS. 12A-12D. For example, a cut-metal-gate(CMG) may be formed, the details of which are discussed in U.S. patentapplication Ser. No. 16/021,344, filed on Jun. 28, 2018, and entitled“Method And Device For Forming Cut-Metal-Gate Feature”, the content ofwhich is incorporated herein for its entirety. For reasons ofsimplicity, these other processes are not discussed in detail herein.

Referring now to FIGS. 13A-13D, a planarization process such as achemical mechanical polishing (CMP) process is performed to the FinFETdevices 100A-100D. The planarization process removes portions of thedielectric layers 400A-400D and portions of the dielectric layers330B-330D. The planarization process is performed until the ILD layers130A-130D are reached. In other words, the ILD layers 130A-130D serve aspolishing-stop layers for the planarization process. At the end of theplanarization process, the upper surfaces of the dielectric layers 400Aare substantially co-planar with the upper surfaces of the ILD layers130A. The FinFET devices 100A-100D also have reduced heights 410A-410D,respectively. In some embodiments, the reduced heights 410A-410D are ina range between about 54 nm and about 64 nm.

As shown in FIG. 13A, the dielectric layers 400A each have a T-shapedcross-sectional profile, since they inherit the cross-sectional profilesof the T-shaped recesses 360A. The dielectric layers 400A also serve as“helmets” for the spacers 150A and the gate electrode (e.g., the metallayers 380A and 140A) below during later etching processes. As such, thedielectric layers 400A may also be referred to as T-shaped helmets 400A.Each T-shaped helmet 400A has an upper portion 400A-U and a lowerportion 400A-L that is disposed below and narrower than the upperportion. The upper surface of the upper portion 400A-U is coplanar withthe upper surfaces of the ILD layers 130A. The side surfaces of theupper portion are in contact with the side surfaces of the ILD layers130A. The bottom surfaces of the upper portion 400A-U are in contactwith the upper surfaces of the spacers 150A. The side surfaces of thelower portion 400A-L are in contact with the side surfaces of thespacers 150A. The bottom surfaces of the lower portion 400A-L are incontact with the metal layers 380A. The T-shaped helmets 400A are one ofthe unique physical characteristics of the present application.

One of the advantages of the process flow discussed above is that itreduces loss of gate height. Starting with a gate height of 170A-170Dshown in FIGS. 2A-2D (e.g., in a range between about 60 nm and about 120nm), the FinFET devices 100A-100D end up with a gate height of 410A-410Dshown in FIGS. 13A-13D (e.g., in a range between about 54 nm and about64 nm). The loss of gate height is small compared to conventionalprocesses. Another advantage is that the present disclosure reducesloading, for example loading in etching processes. For example,conventional processes may require a bulk tungsten to be formed and thenetched as a part of the gate electrode formation, which leads to loadingproblems, particularly for devices having a big difference in sizes suchas the short channel, middle channel, and long channel devices discussedabove. In comparison, the present disclosure does not form a bulktungsten but rather a thin layer of metal such as the metal layer 160D(e.g., tungsten), as discussed above with reference to FIGS. 2A-2D.Furthermore, the flow of the present disclosure results in similarlateral dimensions of the metal layer 140B/160B-140D/160D, which allowsthe metal layers 140B/160B-140D/160D to be easily etched without causingloading, as discussed above with reference to FIGS. 5A-5D. The resultingU-shape cross-sectional profile of the openings 240B, 240C and 240D isanother unique characteristic of the present disclosure.

Additional fabrication processes may be performed to finish thefabrication of FinFET devices 100A-100D. For example, referring now toFIGS. 14A-14D, source/drain contacts 440A, 440B, 440C, and 440D may beformed for the FinFET devices 100A, 100B, 100C, and 100D, respectively.The source/drain contacts 440A-440D are formed over, and provideelectrical connectivity to the source/drain regions 120A-120D. Thesource/drain contacts 440A-440D may include an electrically conductivematerial such as metal or metal compound. The T-shaped helmets 400Aserve as hard masks—to protect the spacers 150A and/or the gateelectrode therebelow—when contact holes are etched in the formation ofthe source/drain contacts 440A-440D. Due to the high-k materialcomposition of the T-shaped helmets 400A, they may be more resistant toetching and therefore function well as etching hard masks. This isbeneficial for the FinFET device 100A, since its small size means thatit may be prone to overlay issues. When overlay shifts occur, thecontact hole etching processes may expose the spacers 150A and possiblythe gate electrode (e.g., metal layers 140A and 380A) to the etching, ifthe T-shaped helmet 400A had not been formed. Here, the T-shaped helmet400A will protect the spacers 150A and the gate electrode from beingetched, which is another advantage of the present disclosure.

Dielectric layers 450A, 450B, 450C, and 450D are disposed above thesource/drain contacts 440A, 440B, 440C, 440D, respectively. Thedielectric layers 450A-450D may have the same material composition asthe dielectric layers 250B-250D, for example silicon nitride. ILD layers460A, 460B, 460C, and 460D are formed over the dielectric layers 450A,450B, 450C, and 450D, respectively. It is understood that the high-kmaterial composition of the T-shaped helmets 400A is merely an exampleand is not intended to be limiting. In other embodiments, other types ofdielectric materials may be used to implement the T-shaped helmets, aslong as a sufficiently high etching selectivity exists between theT-shaped helmets and the ILD0 layer during the contact hole etchingprocess. It is understood that in some embodiments, following thecontact hole etching process, the high-k materials of the T-shapedhelmets 400A may be replaced by a low-k dielectric material (e.g.,dielectric constant lower than about 4). Thus, the T-shaped helmets 400Ain these embodiments may have a low-k dielectric material composition,rather than a high-k dielectric material composition.

FIGS. 2A-2D to 14A-14D pertain to a first embodiment of the presentdisclosure. A second embodiment of the present disclosure is discussedbelow with reference to FIGS. 15A-15D to 22A-22D. For reasons ofsimplicity and consistency, similar components in both the first andsecond embodiments are labeled the same.

Referring now to FIGS. 15A-15D, the FinFET devices 100A-100D are in asimilar stage of fabrication as the stage shown in FIGS. 2A-2D. Forexample, work function metal layers 140A-140D are formed over the finstructures 110A-110D. Metal layers 160A-160D are formed over the workfunction metal layers 140A-140D. As discussed above, for the middlechannel FinFET device 100C and the long channel FinFET device 100D, thework function metal layers 140C/140D and the metal layers 160C/160D donot completely fill the openings 180C and 180D. Unlike the firstembodiment, however, the dielectric layers 330A-330D are formed over theILD layers 130A-130D, respectively. As discussed above, the dielectriclayers 330A-330D may have different material compositions from the ILDlayers 130A-130D. In some embodiments, the dielectric layers 330A-330Dmay include YSiO_(x), SiN, SiOC, SiCN, or SiOCN.

Referring now to FIGS. 16A-16D, the dielectric layer 210C is formed tofill the opening 180C for the FinFET device 100C, and the dielectriclayers 210D and 220D are formed to fill the opening 180D for the FinFETdevice 100D. As discussed above with reference to FIGS. 3A-3D and 4A-4D,the dielectric layers 210C/210D and 220D are formed by depositionprocesses followed by a planarization process.

Referring now to FIGS. 17A-17D, the dielectric layer 230A is formed overthe FinFET device 100A (as a mask layer). Etching processes 235 are thenperformed (while the dielectric layer 230A protects the FinFET device100A underneath) to partially etch away the metal layers 160B-160D andthe work function metal layers 140B-140D of the FinFET devices100B/100C/100D. As a result of the etching processes 235, the openings240B, 240C, and 240D are formed, which may be said to have “U-shaped”cross-sectional profiles. The lateral dimensions 245B, 245C, and 245D ofthe openings 240B, 240C, and 240D are not too substantially differentfrom one another, and thus the etching load concerns are substantiallyreduced.

Referring now to FIGS. 18A-18D, the dielectric layers 250B-250D areformed to fill the openings 240B-240D, respectively. A planarizationprocess is then performed to planarize the upper surfaces of thedielectric layers 250B-250D. The planarization process removes thedielectric layer 230A, as well as portions of the work function metallayer 140A disposed over the dielectric layers 330A. After theplanarization process, the upper surfaces of the dielectric layers250B-250D are substantially coplanar with the upper surfaces of the330B-330D.

Referring now to FIGS. 19A-19D, the T-shaped recess 360A is etched inthe FinFET device 100A. The sidewalls of the T-shaped recess 360A arecollectively defined by the side surfaces of the ILD layers 130A and theside surfaces of the dielectric layers 330A. The metal layer 380A isthen formed over the work function metal layer 140A in the T-shapedrecess 360A.

Referring now to FIGS. 20A-20D, the dielectric layers 400A-400D areformed for the FinFET devices 100A-100D. The dielectric layers 400A-400Dmay include a high-k material such as zirconium oxide (and/or othermaterials). The dielectric layer 400A fills the T-shaped recess 360A.

Referring now to FIGS. 21A-21D, dielectric layers 420A, 420B, 420C, and420D are formed over the dielectric layers 400A, 400B, 400C, and 400D,respectively. In some embodiments, the dielectric layers 420A-420D andthe dielectric layers 210C-210D and 250B-250D may have the same materialcompositions (e.g., silicon nitride). The dielectric layers 420A-420Dmay serve as a hard mask layer for subsequent etching processes such asthe cut-metal-gate (CMG) process discussed in U.S. patent applicationSer. No. 16/021,344, filed on Jun. 28, 2018, and entitled “Method AndDevice For Forming Cut-Metal-Gate Feature”, the content of which isincorporated herein for its entirety. For reasons of simplicity, theseother etching processes are not discussed in detail herein.

Referring now to FIGS. 22A-22D, a planarization process is performed toremove the dielectric layers 420A-420D and portions of the dielectriclayers 400A-400D. The FinFET devices 100A-100D have flat upper surfacesafter the planarization process is performed. The remaining portion ofthe dielectric layer 400A in the FinFET devices 100A forms the T-shapedhelmet.

Similar to the first embodiment discussed above in association withFIGS. 2A-2D through 14A-14D, the second embodiment of FIGS. 15A-15Dthrough 22A-22D have substantially similar device structures, though thefabrication processes performed to reach the end structures are slightlydifferent. The second embodiment still offers the same advantages as thefirst embodiment discussed above.

A third embodiment of the present disclosure is discussed below withreference to FIGS. 23A-23D through FIGS. 28A-28D. Again, for reasons ofsimplicity and consistency, similar components in the first, second, andthird embodiments are labeled the same.

Referring now to FIGS. 23A-23D, the FinFET devices 100A-100D are in asimilar stage of fabrication as the stage shown in FIGS. 2A-2D or thestage shown in FIGS. 15A-15D. For example, work function metal layers140A-140D are formed over the fin structures 110A-110D. The upperportions of the work function metal layers 140A-140D are disposed overthe dielectric layers 330A-330D, respectively. Metal layers 160A-160Dare formed over the work function metal layers 140A-140D. As discussedabove, for the middle channel FinFET device 100C and the long channelFinFET device 100D, the work function metal layers 140C/140D and themetal layers 160C/160D do not completely fill the openings 180C and180D.

Referring now to FIGS. 24A-24D, the dielectric layer 210C is formed tofill the opening 180C for the FinFET device 100C, and the dielectriclayers 210D and 220D are formed to fill the opening 180D for the FinFETdevice 100D. As discussed above with reference to FIGS. 3A-3D and 4A-4D,the dielectric layers 210C/210D and 220D are formed by depositionprocesses followed by a planarization process, which is performed untilthe dielectric layers 330A-330D are exposed.

Referring now to FIGS. 25A-25D, etching processes 235 are performed topartially etch away the metal layers 160A-160D, the work function metallayers 140A-140D, as well as the spacers 150A-150D for all the FinFETdevices 100A-100D. Unlike the first and second embodiments, nodielectric layer mask is formed over the FinFET device 100A to protectit from being etched during the etching processes 235. In other words,all FinFET devices 100A-100D are being etched in the third embodimentshown in FIGS. 24A-24D.

As a result of the etching processes 235, openings 240A-240D are formedin the FinFET devices 100A-100D, respectively. The lateral dimensions245A-245D of their respective openings 240A-240D are not toosubstantially different from one another, and thus the etching loadconcerns are substantially reduced. Note that both the FinFET devices100A-100B have openings 240A-240B that have T-shaped profiles at thispoint.

Referring now to FIGS. 26A-26D, the dielectric layers 400A-400D areformed for the FinFET devices 100A-100D. The dielectric layers 400A-400Dmay include a high-k material such as zirconium oxide. The dielectriclayers 400A-400D fill the openings 240A-240D, respectively.

Referring now to FIGS. 27A-27D, an etching back process is performed topartially remove the dielectric layers 400A-400D. Thereafter, thedielectric layers 420A-420D are formed over the dielectric layers400A-400D for the FinFET devices 100A-100D, respectively. In someembodiments, the dielectric layers 420A-420D include silicon nitride.The dielectric layers 420A-420D may serve as a hard mask layer forsubsequent etching processes such as the cut-metal-gate (CMG) processdiscussed in U.S. patent application Ser. No. 16/021,344, filed on Jun.28, 2018, and entitled “Method And Device For Forming Cut-Metal-GateFeature”, the content of which is incorporated herein for its entirety.For reasons of simplicity, these other etching processes are notdiscussed in detail herein.

Referring now to FIGS. 28A-28D, a planarization process is performed toremove the dielectric layers 400A-400D as well as the dielectric layers330A-330D. After the performance of the planarization process, the uppersurfaces of the ILD layers 130A-130D are substantially coplanar with thedielectric layers 400A-400D, respectively. At this stage of fabrication,the dielectric layers 400A and 400B each have a T-shaped cross-sectionalprofile. In Meanwhile, the dielectric layers 400C and 400D havecross-sectional profiles that resemble a rotated “L” or a flipped “L”.For example, the dielectric layers 400C and 400D each have an upperportion that is wider than a lower portion. One sidewall surface of theupper portion is in contact with the ILD 130C/130D, while an oppositesidewall surface of the upper portion is in contact with the dielectriclayer 210C/210D. One sidewall surface of the lower portion is in contactwith the spacer 150C/150D, while an opposite sidewall surface of thelower portion is in contact with the dielectric layer 210C/210D. Again,the T-shaped profiles of the dielectric layers 400A/400B and therotated/flipped L-shaped profiles of the dielectric layers 400C/400D areunique physical characteristics of the present disclosure, which mayserve as evidence that the fabrication processes discussed above havebeen performed.

As discussed above with the first and second embodiments, additionalfabrication processes may be performed to finish the fabrication ofFinFET devices 100A-100D for the third embodiment. For example,referring now to FIGS. 29A-29D, source/drain contacts 440A-440D may beformed over, and provide electrical connectivity to, the source/drainregions 120A-120D of the FinFET devices 100A-100D, respectively. Due totheir high-k material composition, the dielectric layers 400A-400D serveas hard masks—to protect the spacers gate electrode therebelow—whencontact holes are etched in the formation of the source/drain contacts440A-440D. Dielectric layers 450A-450D are disposed above thesource/drain contacts 440A-440D, respectively. The dielectric layers450A-450D may have the same material composition as the dielectriclayers 250B-250D, for example silicon nitride. ILD layers 460A-460D areformed over the dielectric layers 450A-450D, respectively.

It can be seen that the fabrication processes performed according to thefirst, second, and third embodiments result in a device structure forFinFET device 100A that is substantially the same for all threeembodiments—that is, the T-shaped helmet 400A is present for all threeembodiments. In comparison, the FinFET devices 100B-100D for the thirdembodiment end up with high-k dielectric layers 400B-400D, which is notthe case for the first and second embodiments. As can be seen from FIGS.28B-29B, the high-k dielectric layer 400B for the third embodiment alsohas a T-shaped profile. Meanwhile, as can be seen from FIGS. 28C-28D and29C-29D, the high-k dielectric layers 400C-400D have rotated or flippedL-shaped profiles.

FIGS. 30A, 30B, 30C, and 30D illustrate FinFET devices 100A, 100B, 100C,and 100D fabricated according to a fourth embodiment of the presentdisclosure. The fourth embodiment may follow a substantially similarfabrication flow of the third embodiment, with the exception that thedielectric layers 210C, 210D, and 220D are also formed using a high-kdielectric material, for example, the same material as the high-kdielectric layers 400A-400D, such as zirconium oxide, or other high-kmaterials such as hafnium oxide, zirconium oxide, aluminum oxide,hafnium dioxide-alumina alloy, hafnium silicon oxide, hafnium siliconoxynitride, hafnium tantalum oxide, hafnium titanium oxide, hafniumzirconium oxide, the like, or combinations thereof. As a result, theresulting device structure for all four of FinFET devices 100A-100D willhave a T-shaped helmet 400A-400D, respectively. However, for FinFETdevices 100C-100D, the T-shaped helmets 400C-400D are shaped slightlydifferently. For example, the T-shaped helmet 400C is composed of thedielectric layers 400C and the dielectric layer 210C sandwichedtherebetween. The dielectric layer 210C may have a lower bottom surface(e.g., located further below) than the dielectric layers 400C. Inaddition, though the dielectric layers 400C and 210C may have the samehigh-k material composition (e.g., zirconium oxide) in some embodiments,they may have different material compositions in alternativeembodiments, where the dielectric layers 400C may contain a first typeof high-k dielectric material, while the dielectric layer 210C maycontain a second type of high-k dielectric material different from thefirst type. Likewise, the dielectric layer 210D may have a lower bottomsurface than the dielectric layers 400D, and they may have the same ordifferent material compositions in various embodiments.

FIGS. 31A, 31B, 31C, and 31D illustrate FinFET devices 100A, 100B, 100C,and 100D fabricated according to a fifth embodiment of the presentdisclosure. The fifth embodiment may follow a substantially similarfabrication flow of the first embodiment, with the exception that theFinFET device 100A is fabricated using the same processes as the rest ofthe FinFET devices 100B-100D. For example, in the etching processes 235discussed above with reference to FIGS. 5A-5D, no dielectric layer 230Ais formed as a mask for the FinFET device 100A. Thereafter, no T-shapedhelmets are formed for the FinFET device 100A in this fifth embodiment.In other words, the resulting device structure for the FinFET devices100B-100D are substantially the same for the first embodiment and thefifth embodiment, while the device structure for the FinFET device 100Ais different between the first embodiment and the fifth embodiment, inthat the FinFET device 100 in the fifth embodiment does not have theT-shaped helmet.

FIGS. 32A, 32B, 32C, and 32D illustrate FinFET devices 100A, 100B, 100C,and 100D fabricated according to a sixth embodiment of the presentdisclosure. According to the sixth embodiment, the FinFET device 100Astill has the same structure (e.g., having a T-shaped helmet) as theFinFET device 100A fabricated according to the first embodiment.However, the FinFET devices 100B-100D have different structures in thesixth embodiment, as the thicknesses of the metal layers 160B-160D inthe sixth embodiment are significantly greater than the metal layers160B-160D in the first embodiment.

FIGS. 33A, 33B, 33C, and 33D illustrate FinFET devices 100A, 100B, 100C,and 100D fabricated according to a seventh embodiment of the presentdisclosure. According to the seventh embodiment, the FinFET device 100Astill has the same structure (e.g., having a T-shaped helmet) as theFinFET device 100A fabricated according to the first embodiment.However, the FinFET devices 100B-100D have different structures in theseventh embodiment. For example, the thicknesses of the metal layers160B-160D in the seventh embodiment are significantly greater than themetal layers 160B-160D in the first embodiment. In addition, thedielectric layers 400B-400D for the FinFET devices 100B-100D also haveT-shaped profiles in the seventh embodiment. In other words, the seventhembodiment may be viewed as a combination of the first embodiment andthe sixth embodiment.

It is understood that for the first through seventh embodiments, gatecontacts may be formed for the FinFET devices 100A-100D whenappropriate. For example, for circuit applications where a transistor'sgate needs electrical connectivity, gate contacts may be formed byetching a gate contact hole through the dielectric materials (e.g., theT-shaped helmet 400A or the dielectric layers 210B-210D or 250B-250D)disposed over the work function metal layers 140A-140B and the metallayers 160A-160B, and then filling the gate contact hole with a metalmaterial. For reasons of simplicity, these additional processes are notdiscussed in detail herein.

FIG. 34 is a flowchart of a method 600 for fabricating a semiconductordevice in accordance with various aspects of the present disclosure. Themethod 600 includes a step 610 of forming, on a wafer, a first devicethat includes a first semiconductor structure disposed between a firstsource and a first drain and a second device that includes a secondsemiconductor structure disposed between a second source and a seconddrain. A first interlayer dielectric (ILD) and first spacers define afirst opening that exposes the first semiconductor structure. A secondILD and second spacers define a second opening that exposes the secondsemiconductor structure. A first distance separating the first sourceand first drain is less than a second distance separating the secondsource and the second drain.

The method 600 includes a step 620 of forming a first conductive layerover the first device and over the second device. The first conductivelayer completely fills the first opening but partially fills the secondopening.

The method 600 includes a step 630 of forming a second conductive layerover the first conductive layer. The second conductive layer is formedpartially in the second opening but not in the first opening. The firstconductive layer and the second conductive layer have different materialcompositions.

The method 600 includes a step 640 of forming a first dielectricmaterial over the second conductive layer. The first dielectric materialfills the second opening.

The method 600 includes a step 650 of polishing the first dielectricmaterial until the first conductive layer is reached.

The method 600 includes a step 660 of forming a protective mask over aportion of the first conductive layer disposed over the first device.

The method 600 includes a step 670 of etching the second device whilethe first device is protected by the protective mask. The etchingremoves portions of the first conductive layer and the second conductivelayer formed in the second opening.

The method 600 includes a step 680 of etching the first device topartially remove portions of the first conductive layer in the firstopening and to partially remove the first spacers. In some embodiments,the etching of the first device is performed such that an upper surfaceof the first conductive layer is disposed below upper surfaces of thefirst spacers after the first device is etched.

The method 600 includes a step 690 of forming a second dielectricmaterial over remaining portions of the first conductive layer and thefirst spacers after the etching of the first device. In someembodiments, the second dielectric material has a greater dielectricconstant than the first dielectric material.

It is understood that additional process steps may be performed before,during, or after the steps 610-690 discussed above to complete thefabrication of the semiconductor device. For example, before the step610 is performed, the method 600 may include forming dummy gatestructures (e.g., a polysilicon gate electrode) and removing the dummygate structures to form the first opening and the second opening. Afterthe step 690 is performed, the method 600 may include the formation ofsource/drain contacts of the semiconductor device and/or the formationof vias/metal lines. Other steps may be performed but are not discussedherein in detail for reasons of simplicity.

In summary, the present disclosure utilizes various embodiments eachhaving unique fabrication process flows to form T-shaped helmets withhigh-k dielectric materials over the gate spacers and gate electrodes.The present disclosure also forms similarly-sized (laterally) U-shapedopenings for short channel, middle channel, and long channel devices.Through these U-shaped openings, layers of a metal gate electrode can beetched, for example simultaneously. Based on the above discussions, itcan be seen that the present disclosure offers advantages overconventional semiconductor devices and the fabrication thereof. It isunderstood, however, that other embodiments may offer additionaladvantages, and not all advantages are necessarily disclosed herein, andthat no particular advantage is required for all embodiments. Oneadvantage is that the present disclosure reduces etching loadingconcerns. For example, due to the similar lateral dimensions between theU-shaped openings for the short channel, middle channel, and longchannel devices, the metal layers of the metal gate electrode for thesedevices have lateral dimensions that are not too different from oneanother. This means that they can all be etched simultaneously withoutcausing loading problems. Another advantage is that the T-shaped helmetscan protect the spacers and the gate electrodes below from being etchedinadvertently during subsequent contact hole etching processes. This iseven more beneficial for the short channel device, since it may be moreprone to overlay shift issues due to its smaller size. Here, even ifthere is poor overlay, the high-k dielectric material composition of theT-shaped helmets can adequately protect the spacers (e.g., containing alow-k material) and the metal gate electrode therebelow from beingetched. Other advantages include compatibility with existing fabricationprocess flows, etc.

The advanced lithography process, method, and materials described abovecan be used in many applications, including fin-type field effecttransistors (FinFETs). For example, the fins may be patterned to producea relatively close spacing between features, for which the abovedisclosure is well suited. In addition, spacers used in forming fins ofFinFETs, also referred to as mandrels, can be processed according to theabove disclosure.

One aspect of the present disclosure involves a semiconductor device.The semiconductor device includes a first source component and a firstdrain component. The semiconductor device includes a first semiconductorstructure disposed between the first source component and the firstdrain component. The semiconductor device includes a first gateelectrode disposed over the first semiconductor structure. Thesemiconductor device includes a first dielectric structure disposed overthe first gate electrode. The first dielectric structure has a T-shapedprofile in a cross-sectional view.

One aspect of the present disclosure involves a semiconductor device.The semiconductor device includes a first transistor and a secondtransistor. The first transistor includes: a first source and a firstdrain separated by a first distance; a first semiconductor structuredisposed between the first source and the first drain; a first gateelectrode disposed over the first semiconductor structure; and a firstdielectric structure disposed over the first gate electrode. The firstdielectric structure has a lower portion and an upper portion that isdisposed over the lower portion and is wider than the lower portion. Thesecond transistor includes: a second source and a second drain separatedby a second distance that is greater than the first distance; a secondsemiconductor structure disposed between the second source and thesecond drain; a second gate electrode disposed over the secondsemiconductor structure; and a second dielectric structure disposed overthe second gate electrode. The second dielectric structure and the firstdielectric structure have different material compositions.

Another aspect of the present disclosure involves a method offabricating a semiconductor device. On a wafer, a first device and asecond device are formed. The first device includes a firstsemiconductor structure disposed between a first source and a firstdrain. The second device includes a second semiconductor structuredisposed between a second source and a second drain. A first interlayerdielectric (ILD) and first spacers define a first opening that exposesthe first semiconductor structure. A second ILD and second spacersdefine a second opening that exposes the second semiconductor structure.A first distance separating the first source and first drain is lessthan a second distance separating the second source and the seconddrain. A first conductive layer is formed over the first device and overthe second device. The first conductive layer completely fills the firstopening but partially fills the second opening. A second conductivelayer is formed over the first conductive layer. The second conductivelayer is formed partially in the second opening but not in the firstopening. The first conductive layer and the second conductive layer havedifferent material compositions.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of semiconductor fabrication,comprising: providing a device that includes a semiconductor structure,a source/drain, an interlayer dielectric (ILD) disposed over thesource/drain, and spacers disposed on sidewalls of the ILD, wherein thesemiconductor structure is exposed by an opening; completely filling theopening with a first metal layer; forming a second metal layer over thefirst metal layer; forming a first dielectric layer over the secondmetal layer; performing a planarization process that removes the firstdielectric layer and the second metal layer, wherein the planarizationprocess exposes an upper surface of the first metal layer; forming aprotective mask over the first metal layer; and performing an etchingprocess while the protective mask protects the first metal layer frombeing etched.
 2. The method of claim 1, wherein the filling the openingwith the first metal layer is performed such that portions of the firstmetal layer are formed over the ILD.
 3. The method of claim 1, furthercomprising, after the performing the etching process: partially removingthe ILD and the spacers to form a T-shaped opening; partially fillingthe T-shaped opening with a third metal layer; and completely fillingthe T-shaped opening with a second dielectric layer that has a greaterdielectric constant than the first dielectric layer.
 4. The method ofclaim 3, wherein the partially removing the ILD and the spacers furthercomprises: performing a first etch-back process on the first metallayer; etching away the spacers partially after the first etch-backprocess has been performed; and performing a second etch-back process onthe first metal layer after the etching away the spacers partially. 5.The method of claim 3, wherein: the completely filling the opening witha first metal layer comprises depositing a work function metal layer asthe first metal layer; and the partially filling the T-shaped openingwith the third metal layer comprises depositing tungsten as the thirdmetal layer.
 6. The method of claim 3, wherein the partially filling theT-shaped opening with the third metal layer is performed such that anupper surface of the third metal layer is located below upper surfacesof the spacers.
 7. A method of semiconductor fabrication, comprising:providing a device that includes a semiconductor structure, asource/drain, an interlayer dielectric (ILD) disposed over thesource/drain, and spacers disposed on sidewalls of the ILD, wherein thesemiconductor structure is exposed by an opening; forming a first metallayer in the opening, wherein the first metal layer contains a workfunction metal; forming a second metal layer over the first metal layer,wherein the second metal layer is formed outside the opening; forming afirst dielectric layer over the second metal layer; polishing the firstdielectric layer and the second metal layer until an upper surface ofthe first metal layer is exposed; forming a protective mask over theexposed upper surface of the first metal layer; performing a firstetching process while the protective mask protects the first metal layerfrom being etched; performing a plurality of second etching processes tothe ILD and the spacers to form a T-shaped opening defined by remainingportions of the ILD and the spacers; forming a third metal layer in theT-shaped opening; and forming a second dielectric layer over the thirdmetal layer in the opening, wherein the second dielectric layer has agreater dielectric constant than the first dielectric layer.
 8. Themethod of claim 7, wherein the performing the plurality of secondetching processes comprises: performing a first etch-back process to thefirst metal layer; etching away the spacers partially after the firstetch-back process has been performed; and performing a second etch-backprocess on the first metal layer after the etching away the spacerspartially.